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Mössbauer studies of solid solution systems of Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P
J. inorg,nucl.Chem. 1973.Vol.35, pp. 1219-1225. PergamonPress. Printedin Great Britain
MOSSBAUER STUDIES OF SOLID SOLUTION S Y S T E M S O F F e ( P , As), ( F e , C o ) P , ( F e , M n ) P A N D (Fe, W)P Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A Faculty of Science, Kyushu University, Hakozaki, Fukuoka, Japan (Received 5 January 1972)
A b s t r a c t - T h e M6ssbauer spectra of the solid solution systems Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P, which form an isomorphous MnP structure distorted from NiAs, have been studied. The data could be correlated with the crystal parameters. In (Fe, Co)P as the c-axis is prolonged the quadrupole splitting decreases. INTRODUCTION
THE CHANGESin M6ssbauer spectra in a series of mixed crystals Fe(PO4, AsO4) 2H20 were previously reported by the present authors[l]. In those systems the effect of replacement of anion was found to be small because of the fairly large distance between replacing anions and the cations. In this study systems in which the replacing atoms are more directly bound to the iron were selected, i.e. solid solution systems such as Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P. The solid solution systems described above are isostructural and form a series of solid solutions. Measurements of the M6ssbauer effect in these solid solution systems are of interest for determining the changes of M6ssbauer parameters produced by substitution of the atoms surrounding the iron atoms and for studying the crystallographic structure of these intermetallic compounds. The valency states of these compounds have also been studied. Goodenough's theory[2] for the transition metal monophosphides is generally accepted to account for the lattice energies of these compounds. The formal valency in the monophosphide has been taken to be M3+P3-. The B31 type structure studied in the present investigation is an orthorhombically distorted derivative of the hexagonal B8(NiAs) structure. Each metal atom is surrounded by six phosphorus atoms in a highly distorted octahedron, where the phosphorus atom is surrounded by six metal atoms at the comers of a distorted triangular prism. The B31 phase is divided into two classes, in one of which, denoted B31(1), the ratio c/b is greater than ~ the other is denoted B3 l(k), and the ratio is smaller than V~. FeP, MnP and WP belong to the B31(1) type and only CoP is of the B31(k) type. Schubert[3] pointed out that B31(1) seemed to be stable at lower electron concentration, and B3 l(k) at higher electron concentration. 1. Y. Takashima and Y. Maeda, J. inorg, nucl. Chem. 31, 1337 (1969). 2. J. B. Goodenough, Phys. Rev. 117, 1442 (1960). 3. K. Schubert, Z. Naturforsch. 12, 310 (1957). 1219
1220
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A EXPERIMENTAL
The specimens of phosphide or arsenide were all prepared by heating a mixture of the elements (red phosphorus:components soluble in HCI were removed, metals:purity higher than 99.5%) at 1000°C for 1 day. Specimens thus obtained were crushed to a fine powder and the heating process repeated in a vacuum ampoule at 1000°C for a further 24 hr or more. The products were quickly cooled to room temperature. All the specimens prepared were checked by X-ray powder diffraction patterns with a Rigaku-Denki X-ray diffractometer using Fe-K~ radiation. X-ray powder diffraction patterns of (Fe, Co)P and (Fe, W)P were taken with sodium chloride as an internal calibration standard. Usually, it is difficult to prepare the metal phosphides with exactly stoichiometric composition. The composition of these alloys was determined on the basis of the weights of the starting materials. Some uncertainty may arise because of weight loss during the heating process in the ampoule. The M/Sssbauer spectra were recorded either on a drive system which has already been described[l] or in time mode operation with a 400 channels pulse height analyser driven by pulses from a IwasakiTsushinki PG-2101 pulse generator which produces 5000 cycle pulses. 57Co in Pd foil was used as a source. The source was maintained at room temperature. The Mrssbauer absorption spectra have been taken at room and liquid nitrogen temperature using powdered samples mixed with boron nitride as a binder. The quadrupole splitting of sodium nitroprusside (1.71 mm/sec) was used for velocity calibration. Isomer shifts are quoted with respect to sodium nitroprusside. The X-ray diffraction patterns of the solid solution Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P showed that uniform solid solutions were produced and no lines of the end members were observed in these solid solutions. However, weak foreign lines due to M2P were observed. RESULTS AND DISCUSSION
Typical examples of the Mrssbauer spectra for the intermetallic compounds are shown in Figs. 1 and 2. The Mrssbauer parameters of a number of iron phosphides and arsenides are plotted as a function of iron concentration in Figs. 3-6. The estimated errors are +0.03 mm/sec. The Mrssbauer absorption for the sample with the composition Fe0.1W0.gP was not observed because of the absorption of the effective y-ray owing to the large mass of tungsten• The most apparent feature is the decrease in the quadrupole splitting with the decrease in iron concentration. The change in quadrupole splitting can be predicted from the change in the lattice constant. The crystal structure of the monophosphides of the transition elements have been studied by Stig Rundqvist[4] and R. Fruchart[5]. Acdording to their results the unit cell volume of MnP, FeP, CoP and WP are 98.7, 93.2, 93.1 and 115.9 ,~, respectively. 42
--
."':.
• ..
"~
.,.....
40.....:...,..
U
""
38 I --2'5
I
I
--~aO
--1"5
Doppler
velocityt
I -- I-0
I --0"5
mm/sec
Fig. 1. MiSssbauer absorption of Feo.~Coo.sP at room temperature. 4. S. Rundqvist, Acta chem. scand. 16, 287 (1962).
5. R. Fruchart, Private communication.
1221
MiSssbauer studies of solid solution systems
19 • '.. •.• °.
°•
•.'.'.
~0
18
.. .,." ".,
17
. .°,. .
0
I
o..'•"
I
-2.5
I
-2.0 Doppler
-- 15 velocity,
1
I
-I.0
-0.5
mm/sec
Fig. 2. M6ssbauer absorption of FeP at liquid nitrogen temperature.
0.70
0-50 0
E E
0.70
+
+ + ,
+
+
0-50
0.00
Atomic
1 0"20
I 0"40
fraction M n / ( M n
I 0"60
I 0'80
I I'00
+Fe)
Fig. 3. Quadrupole splitting plotted as a function of iron concentration for (Fe, Mn)P solid solutions.
The quadrupole splitting is expressed by the interaction between the nuclear electric quadrupole moment, Q, and the gradient of the electric field (efg), eq at an iron nucleus as follows:
AE = ½eZgQ ( 1 +~0 2) lt2. The above efg component is divided into two terms. AE = AEval +
AElat.
The subscript "val" refers to the charge distribution of the aspherical 3d "valence" electrons• The subscript "lat" refers to the distribution of the neighboring ions in the crystalline lattice. The component of qval is assumed to be
1222
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A
=. E E
0.70
<3
o.5o
E
E
o.rOo.5oI ++ ,~ ~, ~ ,÷~, ~+~, 0-00
0.20 Atomic
0.40 fraction,
0.60
0.80
I'OO
As/(P+As)
Fig. 4. Quadrupole splitting plotted as a function of iron concentration for Fe(P, As) solid solutions. %
E 0.70
4t
<3 o.50
. • 0-70 E E 0.50
0-oo
I 0-20
I 040
Alomic
I 0-60
fraction,
I o.8o
I I.oo
WI(W+Ee)
Fig. 5. Quadrupole splitting plotted as a function of iron concentration for (Fe, W)P solid solutions.
constant for all the phosphides studied here and to vanish for a reason discussed later. The qlat is affected by the change in the lattice constant. In a crystal with nonoverlapping ions, we can assume the neighboring ions to be point charges. In such crystal, the z z component of AE~at is expressed as follows. AElat = ~ e~ i
(3Z,2 -- r,2) rt5
where e is the charge at the point (x, y, z) and r is the distance between the iron
Mtissbauer studies of solid solution systems
1223
0.70 !
0.50
E E 0"30
÷
<3
0 .I0
0'70 f E E 0.50 I
0.00
I
0'20
0.40
Atomic
I
I
0"60
0"80
froction
I
1.00
Co/ (Co+Fe)
Fig. 6. Quadrupole splitting plotted as a function of iron concentration for (Fe, Co)P
solid solutions.
nucleus and the given nucleus. The component of efg is a function of r. Therefore, if the distance between an iron atom and the neighboring atoms increases, the efg will decrease. However, the magnitude of the quadruople splitting in the solid solution system (Fe, Co)P changes remarkably. The correlation between the cell parameter ratio c/b and the quadrupole splitting in the system (Fe, Co)P is shown in the Fig. 7. A single absorption was observed in the solid solution having composition Fe0.1CoHP near the CoP component. The nearest C o - P distances in
~
0'701
0.50 ,Q
0 -30
0
O
0.10
-I 0"9
I I'00
I 1'02
I 1"04
I 106
I 1-08
c/(b x,/~) Fig. 7. Plots of correlation between the ratio c/(b x 3) and the quadrupole splitting in (Fe, Co)P solid solution.
1224
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A
CoP are 2.21, 2.27, 2.34 and 2.35 fit, and so such a single peak is not expected since the local electric field gradient might be highly distorted at each iron nucleus. At liquid nitrogen temperature the sample showed a single absorption. Therefore, the origin of the electric field gradient lies not only in the symmetry of the atomic sites around the iron nucleus but also in the nature of the chemical bond. If the 3d energy levels are broadened into a band, the electrons are labile and the electric field gradient at an iron nucleus becomes small as does the efg of an alloy. Mott [6] has suggested that there is a critical metal-metal distance Rc such that electrons are labile for R < Re. However, the metal-metal distance in CoP is notably smaller than that in the other phosphides as will be seen in Table 1. In the B8(NiAs) structure some metal-metal distances are less than the critical distance and some are greater. Stein and Walmsley have pointed out that the d band in CoP is overlapped by some state having a phosphorus s orbital component. Increase of cobalt content would bring about greater overlapping in the d band. The isomer shift is a measure of the electron density at the iron nucleus. Differences of electron density at the iron nucleus are due primarily to 4s electrons. Increase in volume will increase the screening of the 4s electrons by the 3d electron of the iron. This fact is supported by the large increase of isomer shift for the system (Fe, W)P. The unit cell volume of WP is much larger than that of the other phosphides. The effect of substitution of phosphorus by arsenic as nearest neighbor to the iron atom is observed in the spectra for the system Fe(P, As). Isomer shifts for the systems (Fe, Mn)P and (Fe, Co)P are almost constant for all compositions. In (Fe, Co)P, the s electrons of phosphorus and d electrons of the metal atom overlap and the electron density at the metal atom nucleus is kept constant. Therefore, the isomer shifts in the system (Fe, Co)P is also almost constant. The isomer shifts relative to iron metal for FeB, FeP and FeAs are 0,08 [8], 0.29 and 0.44 mm/sec, respectively. Cooper et al. [8] suggested that the positive isomer shift is due to the transfer of electrons from boron to iron. That is, they interpreted the isomer shift in terms of an increase of the 3d electron density on the iron atom, because a change in the number of s electrons is more sensitive than that of d electrons to a change in the isomer shift. Table
MnP FeP CoP
1. Metal-metal distances[4] and critical distances[7] for MnP, FeP and CoP R . . . . . (A)
Re(A)
2.70(2), 2.81 (2), 3.17 (2) 2.65(2), 2.79(2), 3-09(2) 2.60(2), 2.75(2), 3.28(2)
3.15 3.12 3-03, 3.18
6. N . F . Mott, Can.J. Phys. 34, 1356 (1956). 7. B.F. Stein and R. H. Walmsley, Phys. Rev. 148 (2), 933 (1966). 8. J. D. Cooper, T. C. Gibb, N. N. Greenwood and R. V. Parish, Trans. Faraday Soc. 60, 2097 (1964).
Mrssbauer studies of solid solution systems
1225
The MiSssbauer spectra of FeP at liquid nitrogen temperature becomes broad and asymmetric. A similar spectrum was reported by Bailey et al. [9], but the reason for this broadening is not clear. A Mrssbauer spectrum with large quadrupole splitting (EQ = 0.62 mm/sec) was observed in the case of Feo.sCo0.sP cooled at liquid nitrogen temperature. This change may indicate some electronic rearrangement or structural change at low temperature. Acknowledgements-The authors express their hearty thanks to Prof. Shunji Umemoto for his continuing encouragement. The authors are also most grateful to Mr. Susumu Shinno for the measurement of X-ray powder diffraction. 9. R.E. Bailey and J. F. Duncan, lnorg. Chem. 6, 1444 (1967).
MOSSBAUER STUDIES OF SOLID SOLUTION S Y S T E M S O F F e ( P , As), ( F e , C o ) P , ( F e , M n ) P A N D (Fe, W)P Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A Faculty of Science, Kyushu University, Hakozaki, Fukuoka, Japan (Received 5 January 1972)
A b s t r a c t - T h e M6ssbauer spectra of the solid solution systems Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P, which form an isomorphous MnP structure distorted from NiAs, have been studied. The data could be correlated with the crystal parameters. In (Fe, Co)P as the c-axis is prolonged the quadrupole splitting decreases. INTRODUCTION
THE CHANGESin M6ssbauer spectra in a series of mixed crystals Fe(PO4, AsO4) 2H20 were previously reported by the present authors[l]. In those systems the effect of replacement of anion was found to be small because of the fairly large distance between replacing anions and the cations. In this study systems in which the replacing atoms are more directly bound to the iron were selected, i.e. solid solution systems such as Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P. The solid solution systems described above are isostructural and form a series of solid solutions. Measurements of the M6ssbauer effect in these solid solution systems are of interest for determining the changes of M6ssbauer parameters produced by substitution of the atoms surrounding the iron atoms and for studying the crystallographic structure of these intermetallic compounds. The valency states of these compounds have also been studied. Goodenough's theory[2] for the transition metal monophosphides is generally accepted to account for the lattice energies of these compounds. The formal valency in the monophosphide has been taken to be M3+P3-. The B31 type structure studied in the present investigation is an orthorhombically distorted derivative of the hexagonal B8(NiAs) structure. Each metal atom is surrounded by six phosphorus atoms in a highly distorted octahedron, where the phosphorus atom is surrounded by six metal atoms at the comers of a distorted triangular prism. The B31 phase is divided into two classes, in one of which, denoted B31(1), the ratio c/b is greater than ~ the other is denoted B3 l(k), and the ratio is smaller than V~. FeP, MnP and WP belong to the B31(1) type and only CoP is of the B31(k) type. Schubert[3] pointed out that B31(1) seemed to be stable at lower electron concentration, and B3 l(k) at higher electron concentration. 1. Y. Takashima and Y. Maeda, J. inorg, nucl. Chem. 31, 1337 (1969). 2. J. B. Goodenough, Phys. Rev. 117, 1442 (1960). 3. K. Schubert, Z. Naturforsch. 12, 310 (1957). 1219
1220
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A EXPERIMENTAL
The specimens of phosphide or arsenide were all prepared by heating a mixture of the elements (red phosphorus:components soluble in HCI were removed, metals:purity higher than 99.5%) at 1000°C for 1 day. Specimens thus obtained were crushed to a fine powder and the heating process repeated in a vacuum ampoule at 1000°C for a further 24 hr or more. The products were quickly cooled to room temperature. All the specimens prepared were checked by X-ray powder diffraction patterns with a Rigaku-Denki X-ray diffractometer using Fe-K~ radiation. X-ray powder diffraction patterns of (Fe, Co)P and (Fe, W)P were taken with sodium chloride as an internal calibration standard. Usually, it is difficult to prepare the metal phosphides with exactly stoichiometric composition. The composition of these alloys was determined on the basis of the weights of the starting materials. Some uncertainty may arise because of weight loss during the heating process in the ampoule. The M/Sssbauer spectra were recorded either on a drive system which has already been described[l] or in time mode operation with a 400 channels pulse height analyser driven by pulses from a IwasakiTsushinki PG-2101 pulse generator which produces 5000 cycle pulses. 57Co in Pd foil was used as a source. The source was maintained at room temperature. The Mrssbauer absorption spectra have been taken at room and liquid nitrogen temperature using powdered samples mixed with boron nitride as a binder. The quadrupole splitting of sodium nitroprusside (1.71 mm/sec) was used for velocity calibration. Isomer shifts are quoted with respect to sodium nitroprusside. The X-ray diffraction patterns of the solid solution Fe(P, As), (Fe, Co)P, (Fe, Mn)P and (Fe, W)P showed that uniform solid solutions were produced and no lines of the end members were observed in these solid solutions. However, weak foreign lines due to M2P were observed. RESULTS AND DISCUSSION
Typical examples of the Mrssbauer spectra for the intermetallic compounds are shown in Figs. 1 and 2. The Mrssbauer parameters of a number of iron phosphides and arsenides are plotted as a function of iron concentration in Figs. 3-6. The estimated errors are +0.03 mm/sec. The Mrssbauer absorption for the sample with the composition Fe0.1W0.gP was not observed because of the absorption of the effective y-ray owing to the large mass of tungsten• The most apparent feature is the decrease in the quadrupole splitting with the decrease in iron concentration. The change in quadrupole splitting can be predicted from the change in the lattice constant. The crystal structure of the monophosphides of the transition elements have been studied by Stig Rundqvist[4] and R. Fruchart[5]. Acdording to their results the unit cell volume of MnP, FeP, CoP and WP are 98.7, 93.2, 93.1 and 115.9 ,~, respectively. 42
--
."':.
• ..
"~
.,.....
40.....:...,..
U
""
38 I --2'5
I
I
--~aO
--1"5
Doppler
velocityt
I -- I-0
I --0"5
mm/sec
Fig. 1. MiSssbauer absorption of Feo.~Coo.sP at room temperature. 4. S. Rundqvist, Acta chem. scand. 16, 287 (1962).
5. R. Fruchart, Private communication.
1221
MiSssbauer studies of solid solution systems
19 • '.. •.• °.
°•
•.'.'.
~0
18
.. .,." ".,
17
. .°,. .
0
I
o..'•"
I
-2.5
I
-2.0 Doppler
-- 15 velocity,
1
I
-I.0
-0.5
mm/sec
Fig. 2. M6ssbauer absorption of FeP at liquid nitrogen temperature.
0.70
0-50 0
E E
0.70
+
+ + ,
+
+
0-50
0.00
Atomic
1 0"20
I 0"40
fraction M n / ( M n
I 0"60
I 0'80
I I'00
+Fe)
Fig. 3. Quadrupole splitting plotted as a function of iron concentration for (Fe, Mn)P solid solutions.
The quadrupole splitting is expressed by the interaction between the nuclear electric quadrupole moment, Q, and the gradient of the electric field (efg), eq at an iron nucleus as follows:
AE = ½eZgQ ( 1 +~0 2) lt2. The above efg component is divided into two terms. AE = AEval +
AElat.
The subscript "val" refers to the charge distribution of the aspherical 3d "valence" electrons• The subscript "lat" refers to the distribution of the neighboring ions in the crystalline lattice. The component of qval is assumed to be
1222
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A
=. E E
0.70
<3
o.5o
E
E
o.rOo.5oI ++ ,~ ~, ~ ,÷~, ~+~, 0-00
0.20 Atomic
0.40 fraction,
0.60
0.80
I'OO
As/(P+As)
Fig. 4. Quadrupole splitting plotted as a function of iron concentration for Fe(P, As) solid solutions. %
E 0.70
4t
<3 o.50
. • 0-70 E E 0.50
0-oo
I 0-20
I 040
Alomic
I 0-60
fraction,
I o.8o
I I.oo
WI(W+Ee)
Fig. 5. Quadrupole splitting plotted as a function of iron concentration for (Fe, W)P solid solutions.
constant for all the phosphides studied here and to vanish for a reason discussed later. The qlat is affected by the change in the lattice constant. In a crystal with nonoverlapping ions, we can assume the neighboring ions to be point charges. In such crystal, the z z component of AE~at is expressed as follows. AElat = ~ e~ i
(3Z,2 -- r,2) rt5
where e is the charge at the point (x, y, z) and r is the distance between the iron
Mtissbauer studies of solid solution systems
1223
0.70 !
0.50
E E 0"30
÷
<3
0 .I0
0'70 f E E 0.50 I
0.00
I
0'20
0.40
Atomic
I
I
0"60
0"80
froction
I
1.00
Co/ (Co+Fe)
Fig. 6. Quadrupole splitting plotted as a function of iron concentration for (Fe, Co)P
solid solutions.
nucleus and the given nucleus. The component of efg is a function of r. Therefore, if the distance between an iron atom and the neighboring atoms increases, the efg will decrease. However, the magnitude of the quadruople splitting in the solid solution system (Fe, Co)P changes remarkably. The correlation between the cell parameter ratio c/b and the quadrupole splitting in the system (Fe, Co)P is shown in the Fig. 7. A single absorption was observed in the solid solution having composition Fe0.1CoHP near the CoP component. The nearest C o - P distances in
~
0'701
0.50 ,Q
0 -30
0
O
0.10
-I 0"9
I I'00
I 1'02
I 1"04
I 106
I 1-08
c/(b x,/~) Fig. 7. Plots of correlation between the ratio c/(b x 3) and the quadrupole splitting in (Fe, Co)P solid solution.
1224
Y O N E Z O M A E D A and Y O S H I M A S A T A K A S H I M A
CoP are 2.21, 2.27, 2.34 and 2.35 fit, and so such a single peak is not expected since the local electric field gradient might be highly distorted at each iron nucleus. At liquid nitrogen temperature the sample showed a single absorption. Therefore, the origin of the electric field gradient lies not only in the symmetry of the atomic sites around the iron nucleus but also in the nature of the chemical bond. If the 3d energy levels are broadened into a band, the electrons are labile and the electric field gradient at an iron nucleus becomes small as does the efg of an alloy. Mott [6] has suggested that there is a critical metal-metal distance Rc such that electrons are labile for R < Re. However, the metal-metal distance in CoP is notably smaller than that in the other phosphides as will be seen in Table 1. In the B8(NiAs) structure some metal-metal distances are less than the critical distance and some are greater. Stein and Walmsley have pointed out that the d band in CoP is overlapped by some state having a phosphorus s orbital component. Increase of cobalt content would bring about greater overlapping in the d band. The isomer shift is a measure of the electron density at the iron nucleus. Differences of electron density at the iron nucleus are due primarily to 4s electrons. Increase in volume will increase the screening of the 4s electrons by the 3d electron of the iron. This fact is supported by the large increase of isomer shift for the system (Fe, W)P. The unit cell volume of WP is much larger than that of the other phosphides. The effect of substitution of phosphorus by arsenic as nearest neighbor to the iron atom is observed in the spectra for the system Fe(P, As). Isomer shifts for the systems (Fe, Mn)P and (Fe, Co)P are almost constant for all compositions. In (Fe, Co)P, the s electrons of phosphorus and d electrons of the metal atom overlap and the electron density at the metal atom nucleus is kept constant. Therefore, the isomer shifts in the system (Fe, Co)P is also almost constant. The isomer shifts relative to iron metal for FeB, FeP and FeAs are 0,08 [8], 0.29 and 0.44 mm/sec, respectively. Cooper et al. [8] suggested that the positive isomer shift is due to the transfer of electrons from boron to iron. That is, they interpreted the isomer shift in terms of an increase of the 3d electron density on the iron atom, because a change in the number of s electrons is more sensitive than that of d electrons to a change in the isomer shift. Table
MnP FeP CoP
1. Metal-metal distances[4] and critical distances[7] for MnP, FeP and CoP R . . . . . (A)
Re(A)
2.70(2), 2.81 (2), 3.17 (2) 2.65(2), 2.79(2), 3-09(2) 2.60(2), 2.75(2), 3.28(2)
3.15 3.12 3-03, 3.18
6. N . F . Mott, Can.J. Phys. 34, 1356 (1956). 7. B.F. Stein and R. H. Walmsley, Phys. Rev. 148 (2), 933 (1966). 8. J. D. Cooper, T. C. Gibb, N. N. Greenwood and R. V. Parish, Trans. Faraday Soc. 60, 2097 (1964).
Mrssbauer studies of solid solution systems
1225
The MiSssbauer spectra of FeP at liquid nitrogen temperature becomes broad and asymmetric. A similar spectrum was reported by Bailey et al. [9], but the reason for this broadening is not clear. A Mrssbauer spectrum with large quadrupole splitting (EQ = 0.62 mm/sec) was observed in the case of Feo.sCo0.sP cooled at liquid nitrogen temperature. This change may indicate some electronic rearrangement or structural change at low temperature. Acknowledgements-The authors express their hearty thanks to Prof. Shunji Umemoto for his continuing encouragement. The authors are also most grateful to Mr. Susumu Shinno for the measurement of X-ray powder diffraction. 9. R.E. Bailey and J. F. Duncan, lnorg. Chem. 6, 1444 (1967).